This invention relates to refractory products for use in the teeming of molten metals and, more particularly, to submerged entry conduit devices for shrouding molten metal flowing under gravity from one vessel to another. The particular characteristic feature of this invention being that the outlet geometry of such devices may be changed to alter and to improve control of the flow of molten metal through the device without exposing the processed melt to additional risks of atmospheric contamination.
Devices to which the invention applies are commonly of a type referred to as submerged entry nozzles, (hereinafter referred to as SEN) and the invention will be further described by reference to such well-known devices. Briefly the function thereof is to shroud molten metal from the atmosphere as it passes from one stage of a casting process to another i.e. from vessel to vessel or from a vessel into the casting mould.
In normal operation they encase the metal stream and penetrate below the level of metal in the lower vessel or mould thus allowing the metal to flow without contact with the external environment.
When combined with a glassy molten mould cover applied to the upper surface of the metal in the mould they provide an excellent means for eliminating the risk of re-oxidation of any reactive constituents of the metal resulting from contact with air.
The flow of molten metal from the SEN must distribute metal evenly into the mould and minimise turbulent flow effects and surface waves that can adversely influence the quality of the cast product.
Much work is directed to selecting the optimum bore and outlet port configuration so as to match the flow characteristics to the mould geometry and casting rates.
As most casting machines must cast a wide range of steel qualities and product sizes at different casting rates, each of which has a specific optimum flow requirement, the selection of a bore and exit port configuration is inevitably a compromise, especially on plants where changes to the order programme can result in a revision to the preferred criteria only a short time before casting occurs and well after the SEN has been set and the other vessel preparations made.
Whilst this compromise provides a technically acceptable operation it does not provide the highest technical standards for every casting combination.
In an attempt to increase flexibility, two component submerged entry systems have been developed where the upper portion is set into the vessel as normal whilst the lower immersed part can be offered against the nozzle of the upper portion at a later stage once the required casting conditions have been established. Various joint configurations are available between the two components but all have the risk of air aspiration through this joint once casting has commenced which increases the risk of re-oxidation, which is detrimental to the steel quality.
An aim of the present invention is to maintain the flexibility for adjustment of the flow characteristics achieved from an exchange nozzle assembly as late as possible in the operational sequence after the precise casting parameters have been established without increasing the risk of air ingress achieved by a conventional one piece SEN assembly. This aim is achievable by the invention described hereafter.
Thus according to one aspect of the present invention there is provided a refractory shroud device having an internal bore for through passage of molten metal, said device comprising, a body defining at least a portion of said bore, and having sufficient length to allow an end thereof to become immersed under normal operational conditions, and operationally engageable with said end a replaceable segment defining outlet means in flow communication with said bore, the said segment having an internal profile adapted to provide a predetermined control over the flow of molten metal from the device.
The submerge pour refractory assembly may be provided as a kit including a plurality of interchangeable submerged end nozzle segments having differing bore sizes, and differences in outlet port configuration such as exit angle, and variations in composition such as use of composite material combinations.
An advantage of this arrangement lies in the fact it provides process flexibility by the ability to exchange outlet segments in response to the exact process parameter requirements, yet the integrity of the casting process is not compromised with regard to contamination by air ingress because the joint between the shroud and outlet component lies below the slag level and is itself immersed in melt.
The manner in which the refractory product is assembled for operational use can be accomplished in a number of ways.
The parts may be formed to have connecting parts having close fitting surfaces such as by provision of a boss on one part and a recess in the adjoining part to provide corresponding surfaces of good fit.
The refractory product is envisaged as most usefully employed as in a sub-entry nozzle.
The design of the SEN remains as standard to below the immersion level. The geometrical adjustments are achieved by changing segments which fit within the lower immersed region and offer various options of bore sizes, exit angles and material combinations which can be introduced into the specially adapted shape of the lower SEN body. By this means the preferred exit flow can be established and as the joints between the two components are immersed below the metal surface in the mould there is no risk of air ingress to cause re-oxidation.
Conveniently, the changeable segment of the nozzle is retained in the body of the nozzle by a push fit mechanism.
Advantageously, the changeable segment of the nozzle is provided with a boss engageable in a corresponding recess in the body of the nozzle.
Alternatively, the changeable segment of the nozzle is retained on the body of the nozzle by a ceramic retainer passing through corresponding apertures in the body and tip of the nozzle.
Advantageously, the changeable segment of the nozzle may be provided with a sump for altering the flow of molten metal from the nozzle.
In another embodiment the desired flow characteristics can be provided by the inclusion of multiple segments within the bore of the nozzle.